Microwave phase correcting network utilizing waveguide coupler having mismatched ports caused by laterally displaced end section

ABSTRACT

A phase correcting network is provided to reduce the nonlinearity of the phase/frequency characteristic of a delay line. The invention is applicable to delay lines which form part of a commutating hybrid. The phase correcting network includes a 3dB coupler which is terminated in a pair of susceptance loaded waveguide stubs.

United States Patent Bodonyi h Aug. 12, 1975 MICROWAVE PHASE CORRECTING[56] References Cited NETWORK UTILIZING WAVEGUIDE UNITED STATES PATENTSCOUPLER HAVING MlSMATCHED PORTS 3,277403 10/1966 Cohn 3. 333/10 x CAUSEDBY LATERALLY DISPLACED END 3,493,898 2/1970 Ward 333 11 SECTION3,727,!52 4/[973 Bodonyi 333/10 X [75] Inventor: Janos Bodonyi,Bicknacre,

England Primary ExaminerPaul L. Gensler Attorney, Agent, or FirmBaldwin,Wight & Brown [73] Asslgneez The Marconi Company Limited,

Ch I f e ms rd, England ABSTRACT [22] Flled: 1974 A phase correctingnetwork is provided to reduce the [2]] Appl N 459,950 non-linearity ofthe phase/frequency characteristic of a delay line. The invention isapplicable to delay lines which form part of a commutating hybrid. Thephase [30] Forelgn Apphcuonrnorny Dam correcting network includes a 3dBcoupler which is May 1973 Umted Kmgdom 2l4SO/73 terminated in a pair ofsusceptance loaded waveguide stubs. [52] US. Cl 333/; 333/28 R; 333/3]A; 333/98 R [51] Int. CIFM. HON H; H01? 5/18; H01P 9/00 [58] Field ofSearch 333/10, ll, 28 R, 31 A, 11 Claims, 6 Drawing Figures PATENTEU AUGI 2 I975 SHEET Q10 mIQ Eu QIQ E46 min 55 QIQ mIu .910 3 6 WNIQ 91m WIQ.010 Elm @Q. aaeaaww QWIQ 31o twin QNIQ 98:6 NNvIu QNIQ 3 UIQPATENTEDAUG 1 2mm 3. 899 756 SHEET 2 PHASE fc FREQUENCY- FIG. 3.

f f2 LOAD 10,

PATENTED AUG I 2l975 SHEET mmqtm f2 FREOUENCY MICROWAVE PHASE CORRECTINGNETWORK UTILIZING WAVEGUIDE COUPLER HAVING MISMATCI-IED PORTS CAUSED BYLATERALLY DISPLACED END SECTION This invention relates to a phasecorrecting network and has particular application in providing improvedchannel centre frequency distribution in commutating hybrid multiplexersat millimetric wave-lengths.

FIG. 1 of the accompanying drawings shows a known form of commutatinghybrid formed of two 3dB couplers each having two inputs and twooutputs. The first 3dB coupler 12 has one input connected to a load andthe other input connected to receive a signal consisting of twofrequencies fl and f2. A first output of the 3dB coupler 12 is directlyconnected to one input of the second 3dB coupler 14, the other output ofthe 3dB coupler l2 being connected to the other input of the 3dB coupler14 by means of a length of waveguide 16 constituting a delay line. Theaction of the commutating hybrid is to separate the components fl and f2of the input signal to the first 3dB coupler l2 and these appear asseparate signals on the respective outputs of the second 3dB coupler 14.

As is well known in the art, the commutating hybrid relies on the factthat the phase delay of the two frequencies fl and f2 will differ afterpassing through the delay line 16 and if the phase difference is an oddmultiple of 11' for one frequency and an even multiple of 1r for theother frequency the two frequencies would be separated.

It is also known, (see for example our copending application Ser. No.157,308, now US. Pat. No. 3,727,152) to connect a plurality of suchcommutating hybrids sequentially in the manner shown in FIG. 2 of theaccompanying drawings so as to provide a multiplexer. The chain shown inFIG. 2 operates in what is believed to be a self-evident manner toseparate l6 channels arriving at the input of the commutating hybrid100. Of course, the operation of the arrangement in FIG. 2 is reversibleand it is possible to feed in sixteen inputs over the respectivechannels CHI to CHI6 by feeding directly into the hybrids h to 10p andto obtain a single output consisting of the combination of these sixteenchannels on the single waveguide connected to the commutating hybrid10a.

FIG. 3 of the accompanying drawings shows the phase delay at the outputof the delay line 16 as a function of frequency. Unlike a coaxialtransmission line, a waveguide does not produce linear phase delay butinstead follows the curve C in FIG. 3 which intersects the frequencyaxis at the point fc corresponding to the cutoff frequency of thewaveguide. Because of the nonlinearity of the curve C it will beappreciated that the frequencies of the channels CH1 to CHI6 cannotfollow an arithmetic progression but instead must follow the curve C. Ifa linear progression is desired, a phase characteristic corresponding tothe line 1, shown in dotted line in FIG. 3, must be followed. It isbelieved that it may be necessary to modify the phase delaycharacteristic of the delay line in the commutating hybrids with a viewto obtaining this linear relationship in order to allow standardizationof the frequencies used in different countries and it is an object ofthe present invention to provide a phase correcting network which may beused in a delay line of a commutating hybrid in a multiplexer to improvethe centre frequency distribution of the multiplexer.

In accordance with the present invention, a phase correcting network forimproving the phase/frequency characteristic of a delay line includes a3dB coupler adapted to be inserted in the said delay line and terminatedin a pair of susceptance loaded waveguide stubs.

Conveniently, the susceptance loading of the waveguide stubs may beeffected by providing one or more mismatches along the length of thestubs, the mismatches being achieved by laterally displacing sections ofthe waveguide relative to one another in the direction of the H-plane.

Each phase correcting network may correct for nonlinearity within apredetermined range of frequencies and if it is desired to providelinearity over a wide range more than one phase correcting network maybe connected in series with one another. It will also be appreciatedfrom the description that follows that phase correcting circuits inaccordance with the invention can be used not only to provide linearitybut generally to modify the phase/frequency characteristics of awaveguide so as to follow a desired configuration within a predeterminedrange of frequencies.

The invention will now be described further, by way of example, withreference to FIGS. 4, 5 and 6 of the accompanying drawings.

FIG. 1 shows a known form of commutating hybrid;

FIG. 2 shows the known connection of a plurality of such commutatinghybrids to form a multiplexer;

FIG. 3 shows the phase delay at the output of the delay line as afunction of frequency;

FIG. 4 is a block diagram of a modified commutating hybrid incorporatinga phase correction circuit in accordance with the invention,

FIG. 5 is a graph generally similar to FIG. 3 showing variations in thephase characteristic of a delay line with variation of the mismatch inthe stubs of the frequency correcting network, and

FIG. 6 is an exploded view of the phase correcting network shown in FIG.4.

Referring now to FIG. 4, a modified commutating hybrid generallydesignated 10' includes two 3dB couplers l2 and 14 the interconnectionsbetween which include a delay line 16. To compensate for thenonlinearity of the phase characteristic in the delay line 16 there isinserted in the latter line a phase correcting network which is enclosedwithin the dotted line and is generally designated 15. The phasecorrecting network 15 includes a 3dB coupler 18 whose inputs areconnected into the delay line 16 and whose outputs are connected tostubs 20 and 22 which are lengths of waveguide terminated in ashort-circuit represented by the symbols S/C in the drawing. Along thelength of each waveguide there is a mismatch 24/26 and whilst only onemismatch is shown in each stub it is to be understood that more than onemay be included if desired.

In order to explain the operation of the phase correcting network 15 inFIG. 4 let it first be assumed that the mismatches 24 and 26 are absent.At the shortcircuited end of the stubs 20 and 22 the electromagneticwave travelling in the waveguide would be reflected and the effect ofthis would be that any signal arriving at the 3dB coupler 18 from the3dB coupler 12 will be passed by the 3dB coupler 18 to the 3dB coupler14 after a phase delay corresponding to twice the length of the stub 20.In effect, the wave arriving at one input of the 3dB coupler is splitequally between the stubs 20 and 22 and upon deflection from theshortcircuited ends of the stubs 20 and 22 the waves combine again toprovide constructive interference at the other input of the 3dB coupler18. If now the effect of the mismatches is considered, it will berealized that standing waves are set up within the stubs 20 and 22 andthe effect of each mismatch will depend upon the intensity of theelectric and magnetic waves at that point and this will in turn dependon the frequency. Thus, for certain frequencies where the electric andmagnetic fields are a minimum at the location of the mismatch themismatch will be of little effect whereas where the electric andmagnetic fields are a maximum there will be partial reflection at themismatch and this will shorten the phase delay of the signals receivedafter reflection. The effect of various mismatches is shown in FIG. 5,in which the basic curve C has been modified to the curves C and C byincluding mismatches of different susceptance within the stubs 20 and22. It will be seen that where the mismatch has positive susceptance +jBthe modified phase characteristic is more curved than the curve C but inthe same sense whereas if the susceptance is negative the curvature isin the oppposite sense. It will be appreciated that by suitably choosinga negative susceptance it is possible to approach the ideal lineardotted line I within the range f1 and f2 in FIG. 5.

The physical construction of the phase correcting network will now bedescribed with reference to FIG.

6. Two grooves 30 and 32 are machined in copper blocks 34 and 36 whichupon mating together define two rectangular waveguides. The blocks 34and 36 are provided with holes 38 through which bolts are passed to keepthe blocks together. Slots 40 are formed in the dividing wall 42 betweenthe grooves 30 and 32 and this provides for energy transfer between thewaveguides and, as is known, such an arrangement can constitute a 3dBcoupler. The ends of the waveguides 30 and 32 to the right of the slotsin the drawing constitute the inputs to the 3dB coupler and the otherends of these waveguides constitute the outputs. Secured to the end ofthe blocks 34 and 36 is a further block 44 which is formed with blindrectangular bores 46 having the same dimensions as the waveguides.Elongate slots 48 are formed in the block 44 and bolts pass throughthese slots into the blocks 34 and 36 to secure the block 44 inposition. The stubs are thus constituted by the shortcircuitedwaveguides which terminate in the block 44 and the mismatch may beachieved by laterally moving the block 44 in an up and down direction asviewed relative to the blocks 34 and 36 so as to provide a mismatchbetween the sections of the stubs inside and outside the block 44.

I claim:

1. A phase correcting network for improving the phase/frequencycharacteristic of a delay line including a 3dB coupler adapted to beinserted in the said delay line and terminated in a pair of shortcircuited waveguide stubs, each of said waveguide stubs beingsusceptance loaded by means of at least one mismatch achieved bylaterally displacing sections of the waveguide relative to one anotherin the direction of the H- plane.

2. A phase correcting arrangement comprising a plurality of phasecorrecting networks as claimed in claim 1 connected in series with oneanother.

3. A phase correcting network for improving the phase/frequencycharacteristic of a delay line comprising in combination a 3dB couplerhaving two input ports and two output ports, said two input ports beingconnected into the delay line for the purpose of transporting signals toand from said delay line; and

first and second waveguide means, each connected to one of said twooutput ports and each terminating in a common short circuit so that anysignal arriving at one input port of said 3dB coupler is split equallybetween said two waveguide means and, upon deflection from the shortcircuit terminations of said waveguide means, the split signalsrecombine in said 3dB coupler so as to provide constructive interferenceat the second input port of said 3dB coupler, said waveguide meansimposing on said recombined signal a phase delay which, without furthermodification to said waveguide means, is non-linear in relationship tothe frequency;

wherein said first and second waveguide means are adapted to besubjected to at least one mismatch caused by the lateral displacement ineach waveguide means of one section of said waveguide means with respectto the other section of said waveguide means in the direction of theplane of the magnetic field of the signal, said mismatches havingsusceptances of such polarity and magnitude as to cause thephase-frequency characteristic of the delay line to become linear innature.

4. A phase correcting arrangement comprising a plurality of phasecorrecting networks as claimed in claim 3 connected in series with oneanother.

5. A phase correcting network as recited in claim 3 wherein said firstand second waveguide means are rectangular in cross section and areformed by the mating of two copper blocks, into each of which there ismachined a rectangular groove.

6. A phase correcting network as recited in claim 5 wherein the shortcircuiting termination of said waveguide means comprises a furthercopper block containing rectangular bores, one for each waveguide meansand of the same dimension as said waveguide means, and so positioned atthe opposite end of said waveguide means from said 3dB coupler that saidwaveguide means may be subjected to lateral mismatch by moving saidfurther copper block in a direction perpendicular to said waveguidemeans.

7. [n a commutating hybrid network which includes a first 3dB couplerhaving two input ports, one connected to a load and the other connectedto receive a multifrequency signal, and two output ports;

a second 3dB coupler having two input ports, a first input portconnected directly to the first output port of said first coupler and asecond input port connected indirectly to the second output port of saidfirst coupler, and two output ports for transmitting two output signals;

and a delay line means in the connection between the second output portof said first coupler and the second input port of said second couplerto form the indirect connection therebetween so that a multifrequencysignal transmitted by the second output port of said first coupler andpassing through said delay line means undergoes separation intocomponent signals so as to introduce a phase delay between saidcomponent signals, with the relationship between the phase delay and thefre uency being non-linear in nature;

the improvement wherein said delay line means comprises a phasecorrecting network which includes a third 3dB coupler having two inputports, a first input port connected to the second output of said firstcoupler, and a second input port connected to the second input port ofsaid second coupler, and two output ports; and

first and second waveguide means, each connected to one of the outputports of said third 3dB coupler and terminated in a short circuit, andeach adapted to be subjected to at least one mismatch caused by thelateral displacement in each waveguide means of at least one section ofsaid waveguide means with respect to the other section of said waveguidemeans in the direction of the plane of the magnetic field of the signal,said mismatches having susceptances of such polarity and magnitude as tocause the phase-frequency characteristic of the delay line to becomelinear in nature.

8. Apparatus for combining and for separating a plurality of signalswhose frequencies are distributed within a given range of frequencies,comprising in combination:

an array of commutating hybrids, each hybrid comprising first and secondwaveguide means for defining a pair of ports at one end of the hybridand a further pair of ports at the other end of the hybrid in which oneof said ports defines a load termination, a first 3dB coupler connectedbetween said first and second waveguide means at said one end of thehybrid and a second 3dB coupler connected between said first and secondwaveguide means at said other end of the hybrid to define apredetermined waveguide length between said couplers within said firstwaveguide means. said second waveguide means defining a delay linebetween said couplers having a length greater than said predeterminedlength;

said second waveguide means comprising separate waveguide sections and afurther 3dB coupler connecting such sections to provide a pair ofwaveguide stubs, and means terminating said waveguide stubs in shortcircuits whereby to provide susceptance loading of said stubs, at leastone of said stubs having a mismatch along its length to providesusceptance loading which establishes a desired phase-frequencycharacteristic of the distribution of said frequencies within saidrange.

9. Apparatus as defined in claim 8 wherein said mismatch is effected byseparating said one stub into two sections, one of which is displacedrelatively to the other in the direction of the H-plane.

10. Apparatus as defined in claim 8 including a second mismatch alongthe length of the other waveguide stub, one mismatch establishingpositive susceptance loading and the second mismatch establishingnegative susceptance loading, the two loadings being related so as toprovide a linear phase-frequency characteristic for said frequencies.

11. Apparatus as defined in claim 10 wherein said stubs are parallel andsaid mismatches are effected by separating said stubs into two sectionswhich are displaced relatively to each other in the direction of theH-plane.

* a it

1. A phase correcting network for improving the phase/frequencycharacteristic of a delay line including a 3dB coupler adapted to beinserted in the said delay line and terminated in a pair of shortcircuited waveguide stubs, each of said waveguide stubs beingsusceptance loaded by means of at least one mismatch achieved bylaterally displacing sections of the waveguide relative to one anotherin the direction of the H-plane.
 2. A phase correcting arrangementcomprising a plurality of phase correcting networks as claimed in claim1 connected in series with one another.
 3. A phase correcting networkfor improving the phase/frequency characteristic of a delay linecomprising in combination a 3dB coupler having two input ports and twooutput ports, said two input ports being connected into the delay linefor the purpose of transporting signals to and from said delay line; andfirst and second waveguide means, each connected to one of said twooutput ports and each terminating in a common short circuit so that anysignal arriving at one input port of said 3dB coupler is split equallybetween said two waveguide means and, upon deflection from the shortcircuit terminations of said waveguide means, the split signalsrecombine in said 3dB coupler so as to provide constructive interferenceat the second input port of said 3dB coupler, said waveguide meansimposing on said recombined signal a phase delay which, without furthermodification to said waveguide means, is non-linear in relationship tothe frequency; wherein said first and second waveguide means are adaptedto be subjected to at least one mismatch caused by the lateraldisplacement in each waveguide means of one section of said waveguidemeans with respect to the other section of said waveguide means in thedirection of the plane of the magnetic field of the signal, saidmismatches having susceptances of such polarity and magnitude as tocause the phase-frequency characteristic of the delay line to becomelinear in nature.
 4. A phase correcting arrangement comprising aplurality of phase correcting networks as claimed in claim 3 connectedin series with one another.
 5. A phase correcting network as recited inclaim 3 wherein said first and second waveguide means are rectangular incross section and are formed by the mating of two copper blocks, intoeach of which there is machined a rectangular groove.
 6. A phasecorrecting network as recited in claim 5 wherein the short circuitingtermination of said waveguide means comprises a further copper blockcontaining rectangular bores, one for each waveguide means and of thesame dimension as said waveguide means, and so positioned at theopposite end of said waveguide means from said 3dB coupler that saidwaveguide means may be subjected to lateral mismatch by moving saidfurther copper block in a direction perpendicular to said waveguidemeans.
 7. In a commutating hybrid network which includes a first 3dBcoupler having two input ports, one connected to a load and the otherconnected to receive a multifrequency signal, and two output ports; asecond 3dB coupler having two input ports, a first input port connecteddirectly to the first output port of said first coupler and a secondinput port connected indirectly to the second output port of said firstcoupler, and two output ports for transmitting two output signals; and adelay line means in the connection between the second output port ofsaid first coupler and the second input port of said second coupler toform the indirect connection therebetween so that a multifrequencysignal transmitted by the second output port of said first coupler andpassing through said delay line means undergoes separation intocomponent signals so as to introduce a phase delay between saidcomponent signals, with the relationship between the phase delay and thefrequency being non-linear in nature; the improvement wherein said delayline means comprises a phase correcting network which includes a third3dB coupler having two input ports, a first input port connected to thesecond output of said first coupler, and a second input port connectedto the second input port of said second coupler, and two output ports;and first and second waveguide means, each connected to one of theoutput ports of said third 3dB coupler and terminated in a shortcircuit, and each adapted to be subjected to at least one mismatchcaused by the lateral displacement in each waveguide means of at leastone section of said waveguide means with respect to the other section ofsaid waveguide means in the direction of the plane of the magnetic fieldof the signal, said mismatches having susceptances of such polarity andmagnitude as to cause the phase-frequency characteristic of the delayline to become linear in nature.
 8. Apparatus for combining and forseparating a plurality of signals whose frequencies are distributedwithin a given range of frequencies, comprising in combination: an arrayof commutating hybrids, each hybrid comprising first and secondwaveguide means for defining a pair of ports at one end of the hybridand a further pair of ports at the other end of the hybrid in which oneof said ports defines a load termination, a first 3dB coupler connectedbetween said first and second waveguide means at said one end of thehybrid and a second 3dB coupler connected between sAid first and secondwaveguide means at said other end of the hybrid to define apredetermined waveguide length between said couplers within said firstwaveguide means, said second waveguide means defining a delay linebetween said couplers having a length greater than said predeterminedlength; said second waveguide means comprising separate waveguidesections and a further 3dB coupler connecting such sections to provide apair of waveguide stubs, and means terminating said waveguide stubs inshort circuits whereby to provide susceptance loading of said stubs, atleast one of said stubs having a mismatch along its length to providesusceptance loading which establishes a desired phase-frequencycharacteristic of the distribution of said frequencies within saidrange.
 9. Apparatus as defined in claim 8 wherein said mismatch iseffected by separating said one stub into two sections, one of which isdisplaced relatively to the other in the direction of the H-plane. 10.Apparatus as defined in claim 8 including a second mismatch along thelength of the other waveguide stub, one mismatch establishing positivesusceptance loading and the second mismatch establishing negativesusceptance loading, the two loadings being related so as to provide alinear phase-frequency characteristic for said frequencies. 11.Apparatus as defined in claim 10 wherein said stubs are parallel andsaid mismatches are effected by separating said stubs into two sectionswhich are displaced relatively to each other in the direction of theH-plane.